Philip Hammond
Downing Street says his conduct was a matter for Theresa May.
He has promised to take Britain out of the EU by October 31 “no ifs, no buts”.
Theresa May has formally resigned as prime minister.
He will become prime minister on Wednesday afternoon.
Rory Stewart, who will quit Johnson's cabinet, warns would-be PM doesn't have the numbers.
The five things you need to know about politics today
Hammond is the second cabinet minister to reveal they will quit if Johnson wins the Tory leadership.
Former minister quit government to block Boris Johnson from suspending parliament
Chancellor does not rule out backing an attempt to bring down his own government.